Electrostatically Mediated Attractive Self-Interactions and Reversible Self-Association of Fc-Fusion Proteins.

Attractive self-interactions and reversible self-association are implicated in many problematic solution behaviors for therapeutic proteins, such as irreversible aggregation, elevated viscosity, phase separation, and opalescence. Protein self-interactions and reversible oligomerization of two Fc-fusion proteins (monovalent and bivalent) and the corresponding fusion partner protein were characterized experimentally with static and dynamic light scattering as a function of pH (5 and 6.5) and ionic strength (10 mM to at least 300 mM). The fusion partner protein and monovalent Fc-fusion each displayed net attractive electrostatic self-interactions at pH 6.5 and net repulsive electrostatic self-interactions at pH 5. Solutions of the bivalent Fc-fusion contained higher molecular weight species that prevented quantification of typical interaction parameters (B22 and kD). All three of the proteins displayed reversible self-association at pH 6.5, where oligomers dissociated with increased ionic strength. Coarse-grained molecular simulations were used to model the self-interactions measured experimentally, assess net self-interactions for the bivalent Fc-fusion, and probe the specific electrostatic interactions between charged amino acids that were involved in attractive electrostatic self-interactions. Mayer-weighted pairwise electrostatic energies from the simulations suggested that attractive electrostatic self-interactions at pH 6.5 for the two Fc-fusion proteins were due to cross-domain interactions between the fusion partner domain(s) and the Fc domain.

Delineating the role of cooperativity in the design of potent PROTACs for BTK.

Proteolysis targeting chimeras (PROTACs) are heterobifunctional small molecules that simultaneously bind to a target protein and an E3 ligase, thereby leading to ubiquitination and subsequent degradation of the target. They present an exciting opportunity to modulate proteins in a manner independent of enzymatic or signaling activity. As such, they have recently emerged as an attractive mechanism to explore previously "undruggable" targets. Despite this interest, fundamental questions remain regarding the parameters most critical for achieving potency and selectivity. Here we employ a series of biochemical and cellular techniques to investigate requirements for efficient knockdown of Bruton's tyrosine kinase (BTK), a nonreceptor tyrosine kinase essential for B cell maturation. Members of an 11-compound PROTAC library were investigated for their ability to form binary and ternary complexes with BTK and cereblon (CRBN, an E3 ligase component). Results were extended to measure effects on BTK-CRBN cooperative interactions as well as in vitro and in vivo BTK degradation. Our data show that alleviation of steric clashes between BTK and CRBN by modulating PROTAC linker length within this chemical series allows potent BTK degradation in the absence of thermodynamic cooperativity.

Challenges in Transitioning Cocrystals from Bench to Bedside: Dissociation in Prototype Drug Product Environment.

Tablets containing a theophylline-glutaric acid (TG) cocrystal dissociated rapidly forming crystalline theophylline (20-30%), following storage at 40 °C/75% RH for 2 weeks. Control tablets of TG cocrystal containing no excipients were stable under the same conditions. The dissociation reaction was water-mediated, and the theophylline concentration (the dissociation product), monitored by synchrotron X-ray diffractometry, was strongly influenced by the formulation composition. Investigation of the binary compacts of the TG cocrystal with each excipient revealed the influence of excipient properties (hydrophilicity, ionizability) on cocrystal stability, providing mechanistic insights into a dissociation reaction. Ionizable excipients with a strong tendency to sorb water, for example, sodium starch glycolate and croscarmellose sodium, caused pronounced dissociation. Microcrystalline cellulose (MCC), while a neutral but hydrophilic excipient, also enabled solution-mediated cocrystal dissociation in intact tablets. Magnesium stearate, an ionizable but hydrophobic excipient, interacted with the cocrystal to form a hygroscopic product. The interaction is believed to be initiated in the disordered cocrystal-excipient particle interface. In contrast, the cocrystal was stable in the presence of lactose, a neutral excipient with no tendency to sorb water. The risk of unintended cocrystal dissociation can be mitigated by avoiding contact with water both during processing and storage.

Impact of Solid-State Form on the Disproportionation of Miconazole Mesylate.

Approximately 50% of solid oral dosage forms utilize salt forms of the active pharmaceutical ingredient (API). A major challenge with the salt form is its tendency to disproportionate to produce the un-ionized API form, decreasing the solubility and negatively impacting product stability. However, many of the factors dictating the tendency of a given salt to undergo disproportionation remain to be elucidated. In particular, the role of the solid-state properties of the salt on the disproportionation reaction is unknown. Herein, various solid forms of a model salt, miconazole mesylate (MM), were evaluated for their tendency to undergo disproportionation when mixed with basic excipients, namely tribasic sodium phosphate dodecahydrate (TSPd) and croscarmellose sodium (CCS), and exposed to moderate relative humidity storage conditions. It was observed that the rate and extent of salt disproportionation were significantly different for the various solid forms of MM. As expected, the amorphous salt was highly susceptible to disproportionation, while the dihydrate salt form was resistant to conversion under the conditions tested. In addition, binary excipient blends of amorphous and anhydrous forms exhibited a reduced extent of disproportionation at a higher relative humidity storage condition. This was due to the competitive kinetics between disproportionation to the free base and conversion to the dihydrate salt form. The results of this study provide important insights into the impact of solid-state form on susceptibility to disproportionation that can be utilized for rationally designing robust pharmaceutical formulations.

Delivering on the promise of protein degraders.

Over the past 3 years, the first bivalent protein degraders intentionally designed for targeted protein degradation (TPD) have advanced to clinical trials, with an initial focus on established targets. Most of these clinical candidates are designed for oral administration, and many discovery efforts appear to be similarly focused. As we look towards the future, we propose that an oral-centric discovery paradigm will overly constrain the chemical designs that are considered and limit the potential to drug novel targets. In this Perspective, we summarize the current state of the bivalent degrader modality and propose three categories of degrader designs, based on their likely route of administration and requirement for drug delivery technologies. We then describe a vision for how parenteral drug delivery, implemented early in research and supported by pharmacokinetic-pharmacodynamic modelling, can enable exploration of a broader drug design space, expand the scope of accessible targets and deliver on the promise of protein degraders as a therapeutic modality.

Automated High-Throughput Matrix Assisted Laser Desorption Ionization Mass Spectrometry Methodology for Formulation Assessment of Polyethylene-Glycol-Conjugated Cytokine Proteins.

Biological therapeutics are major contributors to the pharmaceutical pipeline and continue to grow in sales and scope. Additionally, the field's understanding of cancer biology has advanced such that biopharmaceuticals can harness the power of the immune system for oncology treatments. Several of these novel therapeutics are engineered versions of naturally occurring proteins designed to improve therapeutic properties including potency, target engagement and half-life extension. Cytokines, such as interferons and interleukins, are a broad class of signaling proteins which modulate the body's immune response; engineered cytokines have entered the clinic as promising new immuno-oncology therapies. While these therapies hold great promise, their additional structural complexity introduces analytical challenges, and traditional analytical platforms may be ill-suited to effectively assess product development risks. Further, the pharmaceutical industry relies on streamlining approaches for high-throughput experimentation to achieve speed and efficiency for the discovery and development of new modalities. These demands necessitate the use of state-of-the-art techniques to rapidly characterize these new modalities and guide process development and optimization. Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS) is a rapid, sensitive and automatable technique amenable for high-throughput analysis of proteins. In this work, we have developed an automated MALDI-MS platform to prepare, acquire and analyze molecular degradation in engineered PEGylated cytokines formulation samples. This orthogonal technique integrated seamlessly with current developability risk assessment workflows, ultimately enabling selection of a final formulation strategy for clinical development.

Self-Assembly Properties of an Amphiphilic Phosphate Ester Prodrug Designed for the Treatment of COVID-19.

PF-07304814 is a water-soluble phosphate ester prodrug of a small molecule inhibitor for the SARS CoV-2 3CL protease designed for the treatment of COVID-19. The amphiphilicity and self-assembly behavior of the prodrug was investigated computationally and experimentally via multiple orthogonal techniques to better design formulations for intravenous infusion. The self-assembly of PF-07304814 into micellar structures enabled an increase in the solubility of lipophilic impurities by up to 1900x in clinically relevant formulations. The observed solubilization could help extend the drug product shelf-life and in use stability through inhibition of precipitation, without the need for solubilizing excipients. The work presented in this manuscript provides a roadmap for the characterization of prodrug self-assembly and highlights the potential for prodrug modifications to enhance solubility of both active ingredients and impurities and to extend drug product shelf-life.

Optimization of the secondary drying step in freeze drying using TDLAS technology.

The secondary drying phase in freeze drying is mostly developed on a trial-and-error basis due to the lack of appropriate noninvasive process analyzers. This study describes for the first time the application of Tunable Diode Laser Absorption Spectroscopy, a spectroscopic and noninvasive sensor for monitoring secondary drying in laboratory-scale freeze drying with the overall purpose of targeting intermediate moisture contents in the product. Bovine serum albumin/sucrose mixtures were used as a model system to imitate high concentrated antibody formulations. First, the rate of water desorption during secondary drying at constant product temperatures (-22 °C, -10 °C, and 0 °C) was investigated for three different shelf temperatures. Residual moisture contents of sampled vials were determined by Karl Fischer titration. An equilibration step was implemented to ensure homogeneous distribution of moisture (within 1%) in all vials. The residual moisture revealed a linear relationship to the water desorption rate for different temperatures, allowing the evaluation of an anchor point from noninvasive flow rate measurements without removal of samples from the freeze dryer. The accuracy of mass flow integration from this anchor point was found to be about 0.5%. In a second step, the concept was successfully tested in a confirmation experiment. Here, good agreement was found for the initial moisture content (anchor point) and the subsequent monitoring and targeting of intermediate moisture contents. The present approach for monitoring secondary drying indicated great potential to find wider application in sterile operations on production scale in pharmaceutical freeze drying.

Preclinical characterization of an intravenous coronavirus 3CL protease inhibitor for the potential treatment of COVID19.

COVID-19 caused by the SARS-CoV-2 virus has become a global pandemic. 3CL protease is a virally encoded protein that is essential across a broad spectrum of coronaviruses with no close human analogs. PF-00835231, a 3CL protease inhibitor, has exhibited potent in vitro antiviral activity against SARS-CoV-2 as a single agent. Here we report, the design and characterization of a phosphate prodrug PF-07304814 to enable the delivery and projected sustained systemic exposure in human of PF-00835231 to inhibit coronavirus family 3CL protease activity with selectivity over human host protease targets. Furthermore, we show that PF-00835231 has additive/synergistic activity in combination with remdesivir. We present the ADME, safety, in vitro, and in vivo antiviral activity data that supports the clinical evaluation of PF-07304814 as a potential COVID-19 treatment.

Discovery of a Novel Inhibitor of Coronavirus 3CL Protease for the Potential Treatment of COVID-19.

COVID-19 caused by the SARS-CoV-2 virus has become a global pandemic. 3CL protease is a virally encoded protein that is essential across a broad spectrum of coronaviruses with no close human analogs. The designed phosphate prodrug PF-07304814 is metabolized to PF-00835321 which is a potent inhibitor in vitro of the coronavirus family 3CL pro, with selectivity over human host protease targets. Furthermore, PF-00835231 exhibits potent in vitro antiviral activity against SARS-CoV-2 as a single agent and it is additive/synergistic in combination with remdesivir. We present the ADME, safety, in vitro , and in vivo antiviral activity data that supports the clinical evaluation of this compound as a potential COVID-19 treatment.

Effect of excipient properties, water activity, and water content on the disproportionation of a pharmaceutical salt.

Excipients are crucial components of most pharmaceutical formulations. In the case of a solid oral dosage formulation containing the salt form of a weakly ionizable drug, excipient selection is critical, as some excipients are known to cause salt disproportionation (conversion of salt to the free form). Therefore, robust formulation design necessitates an in-depth understanding of the factors impacting salt disproportionation during processing or storage as this can negatively impact product quality and performance. To date, there is an incomplete understanding of key excipient properties influencing salt disproportionation. Specifically, the potential roles of amorphous excipient glass transition temperature and excipient hygroscopicity, if any, on salt disproportionation are still not well understood. Furthermore, the relationship between the compression and the extent of salt disproportionation is an unknown factor. Herein, by utilizing various grades of polyvinylpyrrolidone (PVP), its copolymer, copovidone (PVPVA), and magnesium stearate, a systematic investigation of disproportionation was performed using pioglitazone HCl as a model salt of a weak base. It was observed that there was a poor correlation between excipient hygroscopicity and the rate and extent of disproportionation. However, powder compression into compacts enhanced the rate and extent of disproportionation. This work focused on disproportionation of the salt of a weak base, as basic drugs are more prevalent, however, salts of weak acids may have similar tendencies under relevant conditions. The knowledge gained from this study will help in understanding the role of various excipients with respect to salt disproportionation, paving the way for designing stable salt formulations.

Chemical stability of amorphous materials: specific and general media effects in the role of water in the degradation of freeze-dried zoniporide.

The objective of the present work was to determine whether hydrolysis in a model lyophile was influenced by general media effects with water-changing properties of the medium or via a specific mechanism of water as a reactant. Four formulations of zoniporide and sucrose (1:10) were prepared with variable amounts of sorbitol [0%-25% (w/v) of total solids). These formulations were then equilibrated at 6% and 11% relative humidity using saturated salt solutions. The lyophile cakes were analyzed by differential scanning calorimetery (DSC), (isothermal microcalorimetry (IMC), solid- state nuclear magnetic resonance (ssNMR) spectroscopy, and ultraviolet-visible diffuse reflectance (DFR) spectroscopy. DSC and IMC were used to assess the global molecular mobility. ssNMR relaxation times were measured to access local mobility. The DFR was used to determine the solid-state acidity expressed as the Hammett acidity function. Stability of samples was evaluated at 40°C by monitoring potency and purity by high-performance liquid chromatography (HPLC). Results were interpreted in terms of the various roles of water: media effect, plasticization, polarity, and reactant. The kinetics of hydrolysis was observed to be correlated with either/both specific "chemical" effects, that is, water reactant as well as media effect, specifically global molecular mobility of the matrix. Increase in reaction rate with increase in water content is not linear and is a weaker dependence than in some hydrolytic reactions in organic solvents. A moderate amount of an inert plasticizer, sorbitol, conferred additional stabilization, possibly by restricting the amplitude and frequency of fast motions that are on a small length scale.

Carbon-deuterium rotational-echo double-resonance NMR spectroscopy of lyophilized aspartame formulations.

In this study, changes in the local conformation of aspartame were observed in annealed lyophilized glasses by monitoring changes in the distance between two labeled sites using C-(2)H rotational-echo double-resonance (REDOR) nuclear magnetic resonance (NMR) spectroscopy. Confirmation that the REDOR experiments were producing accurate distance measurement was ensured by measuring the (13)C-(15)N distance in glycine. The experiment was further verified by measuring the REDOR dephasing curve on (13)C-(2)H methionine. (13)C-(2)H REDOR dephasing curves were then measured on lyophilized aspartame-disaccharide formulations. In aspartame-sucrose formulation, the internuclear distances increased upon annealing, which correlated with decreased chemical reactivity. By contrast, annealing had only a minimal effect on the dephasing curve in aspartame-trehalose formulation. The results show that stability is a function of both mobility and local structure (conformation), even in a small molecule system such as lyophilized aspartame-sucrose.

Crystalline, liquid crystalline, and isotropic phases of sodium deoxycholate in water.

Sodium deoxycholate (NaDC) is an important example of bile salts, representing systems with complex phase behavior involving both crystalline and mesophase structures. In this study, properties of NaDC-water mixtures were evaluated as a function of composition and temperature via X-ray diffraction with synchrotron (sXRD) and laboratory radiation sources, water sorption, polarized light, hot-stage microscopy, and freezing-point osmometry. Several phases were detected depending on the composition and temperature, including isotropic solution phase, liquid crystalline (LC) phase, crystalline hydrate, and ice. The LC phase was identified as hexagonal structure by sXRD, with up to 14 high-order reflections detected. The crystalline phase was found to be nonstoichiometric hydrate, based on XRD and water sorption data. The phase diagram of NaDC-water system has been refined based on both results of this study and other reports in literature.

The glass transition and sub-T(g)-relaxation in pharmaceutical powders and dried proteins by thermally stimulated current.

The main goal of the study was to evaluate the applicability of thermally stimulated current (TSC) as a measure of molecular mobility in dried globular proteins. Three proteins, porcine somatotropin, bovine serum albumin, and immunoglobulin, as well as materials with a strong calorimetric glass transition (T(g)), that is, indomethacin and poly(vinypyrrolidone) (PVP), were studied by both TSC and differential scanning calorimetry (DSC). Protein/sugar colyophilized mixtures were also studied by DSC, to estimate calorimetric T(g) for proteins using extrapolation procedure. In the majority of cases, TSC detected relaxation events that were not observed by DSC. For example, a sub-T(g) TSC event (beta-relaxation) was observed for PVP at approximately 120 degrees C, which was not detected by the DSC. Similarly, DSC did not detect events in any of the three proteins below the thermal denaturation temperature whereas a dipole relaxation was detected by TSC in the range of 90-140 degrees C depending on the protein studied. The TSC signal in proteins was tentatively assigned as localized mobility of protein segments, which is different from a large-scale cooperative motions usually associated with calorimetric T(g). TSC is a promising method to study the molecular mobility in proteins and other materials with weak calorimetric T(g).

Solid state 13C NMR investigation of impact of annealing in lyophilized glasses.

The purpose of this study was to investigate the impact of annealing on molecular mobility in lyophilized glasses, composed of a saccharide excipient and a small concentration of aspartame as a model "drug." Changes in molecular dynamics during annealing were monitored through carbon ((13)C) T(1) and T(1 rho) nuclear magnetic resonance relaxation times of the aspartame and the saccharides. Two different saccharides were studied, sucrose and trehalose. The local mobility of the aspartame guest was found to correlate closely with the overall structural relaxation monitored through calorimetric methods in the aspartame: sucrose formulation. In general terms, annealing leads to longer NMR relaxation times, indicating a slowing of the local dynamics. By contrast, annealing had only a minimal effect on the NMR relaxation times in aspartame: trehalose. Specificity of solid state NMR in detecting molecular mobility in guest and host molecules showed that sucrose provided a homogenous matrix for the guest drug as compared to the trehalose.

Investigation of the impact of annealing on global molecular mobility in glasses: optimization for stabilization of amorphous pharmaceuticals.

The purpose of this research was to investigate the effect of annealing on the molecular mobility in lyophilized glasses using differential scanning calorimetry (DSC) and isothermal microcalorimetry (IMC) techniques. A second objective that emerged was a systematic study of the unusual pre-T(g) thermal events that were observed during DSC warming scans after annealing. Aspartame lyophilized with three different excipients; sucrose, trehalose and poly vinyl pyrrolidone (PVP) was studied. The aim of this work was to quantify the decrease in mobility in amorphous lyophilized aspartame formulations upon systematic postlyophilization annealing. DSC scans of aspartame:sucrose formulation (T(g) = 73 degrees C) showed the presence of a pre-T(g) endotherm which disappeared upon annealing. Aspartame:trehalose (T(g) = 112 degrees C) and aspartame:PVP (T(g) = 100 degrees C) showed a broad exotherm before T(g) and annealing caused appearance of endothermic peaks before T(g). This work also employed IMC to measure the global molecular mobility represented by structural relaxation time (tau(beta)) in both un-annealed and annealed formulations. The effect of annealing on the enthalpy relaxation of lyophilized glasses, as measured by DSC and IMC, was consistent with the behavior predicted using the Tool-Narayanaswamy-Moynihan (TNM) phenomenology (Luthra et al., 2007, in press). The results show that the systems annealed at T(g) -15 degrees C to T(g) -20 degrees C have the lowest molecular mobility.

Correlation of annealing with chemical stability in lyophilized pharmaceutical glasses.

This research constitutes a thorough study of the relationship between the chemical stability, aging state and global molecular motion on the one hand, and microscopic local mobility in multi-component systems on the other hand. The objective of the present work was to determine whether annealing a glass below T(g) affects its chemical stability and determine if the rate of chemical degradation couples with global relaxation times determined using calorimetery, and/or with T(1) and T(1rho) relaxation times measured using ssNMR. Model compounds chosen for this research were lyophilized aspartame/sucrose and aspartame/trehalose (1:10 w/w) formulations. The chemical degradation was assessed at various temperatures using high-performance liquid chromatography (HPLC) to determine the impact of annealing on chemical stability. The rate constant for chemical degradation was estimated using stretched time kinetics. The results support the hypothesis that thermal history affects the molecular mobility required for structural relaxation and such effect is critical for chemical stability, that is, a stabilization effect upon annealing is observed.

Effects of annealing on enthalpy relaxation in lyophilized disaccharide formulations: mathematical modeling of DSC curves.

The overall objective of these studies was to investigate, by experimental studies and theoretical analysis, the optimum annealing conditions to obtain maximum structural relaxation in lyophilized glasses of pharmaceutical significance. The model formulations used in this work were aspartame: sucrose and aspartame: trehalose (1:10 w/w) freeze-dried glasses. In this article, structural relaxation in amorphous systems was described in terms of the change in the fictive temperature (T(f)) and was measured using the enthalpy relaxation endotherm in a differential scanning calorimeter (DSC). The theoretical analysis was performed using the Tool-Narayanaswamy-Moynihan (TNM) model. The effect of different annealing conditions (temperature and time) on fictive temperature obtained from the theoretical analysis was calculated and compared with the experimental results. The model reproduced the experimental data very well for samples that were quench cooled from the liquid. However, the model fits were poor for lyophilized samples, indicating an inability to incorporate the complex thermal history of freeze-drying in the TNM model. The optimum aging conditions were determined from both DSC and approximated best-fit parameters of the TNM model, and it was found that annealing when done at a temperature about 15-25 degrees C below T(g) resulted in maximum structural relaxation.